Obesity continues to grow as a modern-day epidemic. Because obesity is a strong risk factor for numerous other metabolic derangements, diabetes, cardiovascular disease, fatty liver disease, various cancers, as well as a host of other morbidities, there is strong motivation to understand the genetic architecture of adiposity traits. Genomewide association scans (GWAS) aimed at adiposity traits recently have produced many findings, implicating numerous novel genes, owing to cooperation of large cohort and family studies in meta-analyses of tens of thousands of subjects. The international Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium (Atherosclerosis Risk in Communities Study (ARIC), the Cardiovascular Health Study (CHS), the Framingham Heart Study (FHS), the Rotterdam Study (RS), and the Age, Gene/Environment Susceptibility-Reykjavik Study (AGES- Reykjavik Study) was convened to promote the discovery of new genes involved in multiple complex traits using GWAS analysis. The Adiposity Working Group includes these cohorts plus the Family Heart Study (FamHS), the European Special Population Network consortium (EUROSPAN), and the Old Order Amish (OOA), together representing over 37,000 subjects. Data on ~8,200 African-Americans are available from the FamHS and the Candidate gene Association Resource (CARe) resource, which includes the Jackson Heart Study, the Cleveland Family Study, ARIC, CARDIA and MESA. These sample sizes enable detection of variants influencing as little as ~0.5% of trait variance. We propose to extend the meta-analysis approach of these cohorts to investigate body mass index (BMI, wt/ht2), waist circumference (WC), waist-hip ratio (WHR), obesity (BMI>30 kg/m2) and extreme obesity (BMI>40 kg/m2). We will address 4 major aims that go beyond primary gene discovery. We propose to contrast the genetic architecture for adiposity traits between European-Americans and African-Americans; to investigate a series of g x e interaction hypotheses, including sex, age, and smoking; to identify adiposity loci with pleiotropic effects on lipid and glucose metabolism traits to deconstruct the correlations among these risk factors; and to identify and test pathways with high impact on adiposity traits, investigating whether the predominant pathways differ by sex and race. For these aims, we will work with studies from the GIANT (Genetic Investigation of ANthropometric Traits) Consortium to augment power, together potentially including up to ~125,000 European- American subjects. We have a unique opportunity to investigate a number of issues using extant GWAS scans to elucidate the genetic architecture of obesity and related traits in two ethnic groups. Findings from these studies will be validated with additional genotyping and / or sequencing, as warranted. This work will stimulate the discovery of variants and pathways, and potentially extend our understanding of the genetic basis of obesity risk and suggest potential therapeutic targets.